Heat Resistance of Ferritic Stainless Steels with 15% Chromium for Automobile Exhaust System

The high-temperature strength and thermal fatigue properties of Fe-Cr-Nb-Mo ferritic stainless steel (FSSNEW) developed for automobile exhaust system were investigated. The results show that the high-temperature tensile strength and yield strength of FSSNEW are better than or equal to those of the presently applied ferritic stainless steels. The thermal fatigue cracks nucleate at the V-notch. The inclusions along grain boundaries become prior regions for initiation of the cracks. The inclusions distributed at the defects make the formation of cracks in the materials easily through the effects of cycle thermal stress and thermal strain. The length and propagated rate of thermal fatigue cracks increase with the maximum tested temperature increasing. When the maximum temperature arrives at 900°C, the high-temperature oxidation is serious along the grain boundaries, which aggravates the cracks propagating along the grain boundaries. The principle mechanism of stress assisted grain boundary oxygen (SAGBO) embrittlement can be applied to illustrate the effects of external stress on aggravating the damage caused by environmental factors. Therefore, the high-temperature oxidation is the main reason for the propagation of thermal fatigue cracks. The FSSNEW is satisfied for the applied requirement of high-temperature strength in the hot side of the automobile exhaust system.

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Thermal Fatigue Crack Initiation of Laser Deposited High-temperature Titanium Alloy Ti60A in 20–700 °C

High Temperature Materials and Processes ◽

10.1515/htmp-2012-0141 ◽

2013 ◽

Vol 32 (4) ◽

pp. 331-337 ◽

Cited By ~ 1

Author(s):

A.L. Zhang ◽

D. Liu ◽

H.M. Wang

Keyword(s):

Titanium Alloy ◽

Fatigue Crack ◽

High Temperature ◽

Crack Initiation ◽

Thermal Fatigue ◽

Fatigue Cracks ◽

Fatigue Crack Initiation ◽

Thermal Fatigue Crack ◽

Fatigue Process ◽

Thermal Fatigue Cracks

AbstractThermal fatigue damage of high-temperature titanium alloys is of great concern for severe temperature-fluctuating environment, and the thermal fatigue crack initiation stage plays a crucial role in thermal fatigue life. In present study, thermal fatigue tests keeping 55 seconds at 700 °C followed by water cooling 15 seconds at 20 °C were performed for the laser deposited high-temperature titanium alloy Ti60A (Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si). Thermal fatigue cracks initiate after 800 thermal fatigue cycles with a length of 20 µm. Subsequently numerous cracks grow to 500 µm and cause severe degradation after 1000 cycles. To investigate the crack initiation behavior, microstructural changes during thermal fatigue process were examined by OM, SEM, EPMA and TEM. Thermal fatigue cracks initiate preferably at grain boundaries, α/β interfaces, microvoids, and abnormal coarsened α produced by oxygen interstitial solution. Mechanisms of thermal fatigue crack initiation are related to compatibility of local deformation and microstructural changes during thermal fatigue process.

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Grain Boundaries and Interfaces in MoSi2 and MoSi2-SiC Composites and Their Effect on High Temperature Strength

Microscopy and Microanalysis ◽

10.1017/s1431927600034619 ◽

2000 ◽

Vol 6 (S2) ◽

pp. 424-425

Author(s):

R. Mitra ◽

W.-A. Chiou ◽

A. Venugopal Rao

Keyword(s):

High Temperature ◽

Grain Boundaries ◽

Weight Fraction ◽

High Temperature Strength ◽

High Melting Point ◽

Temperature Oxidation ◽

Structural Applications ◽

Temperature Fracture ◽

Sic Composites

Molybdenum di-silicides (MoSi2) based materials have a strong potential for high temperature structural applications due to high melting point of 2030°C, outstanding elevated temperature oxidation resistance and limited ductility above a temperature range of 1100-1300°C. The major shortcomings of MoSi2 for structural applications are its poor room temperature fracture toughness and low high temperature strength. Sustained efforts including reinforcing MoSi2 with ceramic reinforcements, alloying and in-situ processing, have been made to improve these properties. The purity of grain boundaries and interfaces, which in turn depends on the processing method plays a significant role in the high temperature properties and this paper aims to show that.Intimately mixed Mo and Si powders (Mo:Si = 63:37 by weight fraction) were reaction hot pressed (“RHP“) in vacuum at 1500°C for 1 h, using a pressure of 26 MPa. During the hot pressing process, Mo and Si reacted to form MoSi2.

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Lattice Imaging of Grain Boundaries in Ceramics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100078171 ◽

1977 ◽

Vol 35 ◽

pp. 114-115

Author(s):

D. R. Clarke ◽

G. Thomas

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

Silicon Nitride ◽

Grain Boundaries ◽

High Temperature Strength ◽

Current Interest ◽

Lattice Imaging ◽

Special Significance ◽

Structural Applications ◽

Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

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AK STEEL 441

Alloy Digest ◽

10.31399/asm.ad.ss0965 ◽

2006 ◽

Vol 55 (6) ◽

Keyword(s):

Stainless Steel ◽

Corrosion Resistance ◽

High Temperature ◽

Tensile Properties ◽

Oxidation Resistance ◽

Ferritic Stainless Steel ◽

High Temperature Oxidation ◽

High Temperature Strength ◽

Temperature Oxidation ◽

Temperature Performance

Abstract AK Steel 441 has good high-temperature strength, an equiaxed microstructure, and good high-temperature oxidation resistance. The alloy is a niobium-bearing ferritic stainless steel. This datasheet provides information on composition, hardness, and tensile properties as well as deformation. It also includes information on high temperature performance and corrosion resistance as well as forming and joining. Filing Code: SS-965. Producer or source: AK Steel.

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Assessment of thermal behavior of a cooling system to reduce thermal fatigue cracks in aluminum injection molds

Revista Liberato ◽

10.31514/rliberato.2020v21n35.p75 ◽

2020 ◽

pp. 75-86

Author(s):

Sergio Antonio Camargo ◽

Lauro Correa Romeiro ◽

Carlos Alberto Mendes Moraes

Keyword(s):

Thermal Fatigue ◽

Cooling System ◽

Fatigue Cracks ◽

Cooling Water ◽

Thermal Conditions ◽

Thermal Gradients ◽

Ansys Software ◽

Cooling Systems ◽

Thermal Fatigue Cracks ◽

Number Of Cycles

The present article aimed to test changes in cooling water temperatures of males, present in aluminum injection molds, to reduce failures due to thermal fatigue. In order to carry out this work, cooling systems were studied, including their geometries, thermal gradients and the expected theoretical durability in relation to fatigue failure. The cooling system tests were developed with the aid of simulations in the ANSYS software and with fatigue calculations, using the method of Goodman. The study of the cooling system included its geometries, flow and temperature of this fluid. The results pointed to a significant increase in fatigue life of the mold component for the thermal conditions that were proposed, with a significant increase in the number of cycles, to happen failures due to thermal fatigue.

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Estimation of Damage to the Collector of a Water Economizer by Thermal Fatigue Cracks

Materials Science ◽

10.1023/b:masc.0000042796.06312.c9 ◽

2004 ◽

Vol 40 (1) ◽

pp. 132-138 ◽

Cited By ~ 1

Author(s):

R. Ya. Kosarevych ◽

O. Z. Student ◽

Ya. D. Onyshchak ◽

A. D. Markov ◽

I. V. Ripei ◽

...

Keyword(s):

Thermal Fatigue ◽

Fatigue Cracks ◽

Thermal Fatigue Cracks ◽

Water Economizer

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In-Situ Monitoring via Synchrotron Radiation Laminography of Thermal Fatigue Cracks at Die-Attached Joints Under Cyclic Energization Loading

ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems ◽

10.1115/ipack2017-74177 ◽

2017 ◽

Cited By ~ 1

Author(s):

Hiroyuki Tsuritani ◽

Toshihiko Sayama ◽

Yoshiyuki Okamoto ◽

Takeshi Takayanagi ◽

Masato Hoshino ◽

...

Keyword(s):

Fatigue Crack ◽

Crack Propagation ◽

Fatigue Crack Propagation ◽

Thermal Fatigue ◽

Fatigue Cracks ◽

In Situ Monitoring ◽

X Ray ◽

Crack Propagation Process ◽

Thermal Fatigue Cracks

Recently, due to the increasing heat density of printed circuit boards (PCBs), thermal fatigue damage in the joints has exerted a more significant influence on the reliability of electronic components. Accordingly, the development of a new nondestructive inspection technology is strongly desired by related industries. The authors have applied a synchrotron radiation X-ray micro-tomography system to the nondestructive observation of micro-cracks. However, the reconstruction of CT images is difficult for planar objects such as PCB substrates, due to insufficient X-ray transmission in the direction parallel to the substrates. In order to solve this problem, a synchrotron radiation laminography system was developed to relax size restrictions on the observation samples, and was applied to the three-dimensional nondestructive evaluation of several kinds of solder joints, which were loaded under accelerated thermal cyclic conditions via thermal shock tests. Moreover, the thermal fatigue crack propagation process that occurs under actual PCB energization loading conditions will differ from that under the usual acceleration test conditions. In this work, the possibility of in-situ monitoring of the thermal fatigue crack propagation process using the laminography system was investigated at die-attached joints subjected to cyclic energization loading, which is close to the actual usage conditions of PCBs. The optical system developed for use in the laminography system was constructed to provide a rotation stage with a tilt from the horizontally incident X-ray beam, and to obtain X-ray projection images via a beam monitor. In this manner, the X-ray beam is sufficiently transmitted through the planar specimen in all projections. The observed specimens included several die-attached joints, in which 3 mm square ceramic dies had been mounted on a 40 mm square FR-4 substrate using Sn-3.0wt%Ag-0.5wt%Cu solder. Consequently, the laminography system was successfully applied to the in-situ monitoring of thermal fatigue cracks that appeared in the solder layer under cyclic energization. This was possible because the laminography images obtained in the energization state have a quality that is equivalent to those obtained in a non-energized state, provided that the temperature distribution of the specimen is stable. In addition, the fatigue crack propagation process can be quantitatively evaluated by measuring the crack surface area and calculating the average crack propagation rate. However, in some cases, the appearance of thermal fatigue cracks was not observed in a solder layer that had been loaded by the accelerated thermal cycle test. This result strongly suggests that delamination occurred at the interface, which indicates that the corresponding fracture mode was significantly influenced by the type of thermal loading.

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